INFECTIOUS mononucleosis is a fairly common disease in the college age group. Spontaneous rupture of the spleen in a case, however, is still of such rarity and importance to warrant reporting it in some detail, together with a review of 45 simil aicases found in the literature. Report of a Case A 21-year-old male student was admitted to the infirmary Oct. 26, 1960, with the chief complaint of fever, sore throat, and fatigue of about a week's duration. Examination revealed a tall, slender male with enlarged, tender cervical lymph nodes, a diffusely reddened pharynx with a few petechial spots on the soft palate, a temperature of 102° F. (38.9° C), pulse rate of 90, and blood pressure level of 100/90 mm. Hg. He was placed on bed rest with acetylsalicylic acid therapy. Over the next 2 days the temperature fluctuated between 99.6° and 102° F. (37.6° and 38.9° C), and